Residential Underpinning Advice

[LogicGate]

I have a crawl space that I am currently planning to underpin. Three walls have 3ft Foundation walls (12" thick) with 2' footing. and one wall has a full 8ft foundation. Dimensions 13' x 22' x 13'

I have area carved up into 4ft sections plan to underpin the full thickness of the footing 2' but each concrete pier. Leave 2" gap between underpinning + existing footing and dry pack after 24hr cure.

Each pier will be 5ft High x 4ft Wide x 2ft Deep and here are my concerns.....

1. Worried about the peir shifting with the lateral pressure form the soil because I hoping not to pour the floor slab for a few months until I decide what I will do with the space and if I will want radiant floor, plumbing etc... I am a bit scared leaving it without a slab...

2. My soil type is a sandy mix... and Im worried about he sheer weight of all the concrete from 2ft Deep (full footing) and 5ft height. My concern is that due to the weight and load that the soil will settle...

Should I be worried?

 

[msquared48]

Yes. I suggest you engage a structural engineer here.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[PEinc]

You need to hire an engineer who is experienced in design and construction of underpinning. The basement floor slab may not prevent the underpinning and the existing foundation wall from overturning and pushing laterally into the basement. The basement floor slab is too low to provide lateral support and prevent overturning. You need to check the underpinned wall for sliding and overturning. This exact question was asked just this week by another person. A lightly loaded building with relatively narrow underpinning piers (+2') will probably not have a great enough safety factor for overturning. Sliding resistance can always be improved, if necessary, by deepening the pier below subgrade of the basement.

http://www.PeirceEngineering.com

 

[LogicGate]

I've tried to find an engineer locally but have not had any luck... Most shops are telling me they only do commercial and the others say the job is to small for them to take on...

FYI: I have a background in construction and engineering I design and build downdraft HVAC systems for clean rooms of various types... I know my way around a job site and familiar with building science. I Was hoping to tackle this myself and manage my concrete contractor.

Would you be comfortable if I doweled rebar vertically every 12" to the with it embedded 8" w/ Sika Epoxy. and also tie piers together horizontally with rebar...

As for footing depth would it be acceptable if i went 1' deeper than the slab height?

Sorry if i am pushing the issue but just trying to make an informed decision with limited resources...

Thank you..

 

[PEinc]

You need an experienced underpinning engineer. We have neither enough information or time online totell you what you should do. Where are you located?

http://www.PeirceEngineering.com

 

[LogicGate]

I am in Queens NY... If you have someone you would recommend I would appreciate it.

Thank you very much

 

[LogicGate]

I am pretty much in the guts of this project (but nothing started as yet) and if you are open to a fee based consultation... I could send you any data you need, do soil compaction test, pictures, measurements, plot plan etc... and any other data you may need.

I would be happy to pay for some qualitative advise on how to proceed and understand that it would be best effort given the constraints of the data I can get to you.

Please let me know if you can help....